This invention relates to reinforced thermoplastic film produced by laminating together at least two strips of oriented thermoplastic film each having the direction of orientation at an angle to each other and having at least one annealed aluminum foil interlaid between the strips with adhesion.
It has been known in the art to sandwich aluminum foil between strips of thermoplastic material for imparting shape stability or rigidity to a laminate as disclosed in U.S. Pat. No. 4,064,302. However, the conventional laminate is not often suitable for the uses intended for ordinary packaging articles, such as for example, bags for which a suitable flexibility and a rupturing resistance against an applied force are usually appreciated.
We have discovered that strips of a thermoplastic film which are lapped but not bonded together often exhibit a higher degree of rupturing resistance against an applied force than do such films which are bonded together. We have found, however, that by employing a reinforcing layer such as an annealed aluminum foil of suitable thickness, the reinforcing layer will rupture as a force of sufficient magnitude is applied thereto so as to provide the desired unbonded condition in certain portions of the laminate. The resulting unbonded areas of the laminate are found minute enough so that the decrease in reinforcing effectiveness of the layer is negligible, while at the same time greatly increasing the laminate's resistance to rupturing. The bonded condition, however, is required, at least initially, to provide the necessary reinforcement for the laminate.